The use of superabsorbent polymer material in disposable diapers is generally known. The use of superabsorbent polymer material facilitates disposable diapers having a thinner absorbent core versus the use of absorbent materials such as fluff pulp, especially while the disposable diaper is in the dry state.
Today, most disposable diapers which are commercially available still have absorbent cores containing a mixture of so-called airfelt (cellulose fibers) and superabsorbent polymer particles. The cellulose fibers comprised by the absorbent core generally hold the superabsorbent polymer particles in place as the cellulose fibers entangle the particles such that the particles are trapped between the cellulose fibers. This generally does not result in a complete immobilization of the superabsorbent polymer particles, as the particles still may have some degree of freedom to move within the interstices between the cellulose fibers. However, the superabsorbent polymer particles are held in the desired position to a sufficiently satisfying degree.
Using higher amounts of superabsorbent polymer particles is desirable as it enables thinner absorbent cores. However, in absorbent cores having high amounts of superabsorbent polymer particles and little or no airfelt, the superabsorbent polymer particles can no longer be held in place in the interstices between the cellulose fibers, as the ratio of superabsorbent polymer particles to cellulose fibers is too high. Therefore, in absorbent cores having very high amounts of superabsorbent polymer particles (such as >80%), the particles have to be immobilized by some other means. One way to facilitate immobilization is the use of adhesive, such as hot melt adhesive. The hot melt adhesive may be applied as a fine, fibrous network within the absorbent core. Further, in absorbent cores having a high percentage of superabsorbent polymer material and little or no airfelt the superabsorbent polymer material is often sandwiched between carrier substrates. The carrier substrates are typically nonwoven webs.
Absorbent cores having relatively high amounts of superabsorbent polymer particles immobilized by hot melt adhesive and having little or no airfelt have few to no interstices (e.g. those provided between cellulose fibers). Thus, there is no available “free space” within the absorbent core into which the superabsorbent polymer particles can expand upon absorption of liquid. In these absorbent cores the superabsorbent polymer particles, upon swelling, will exert a certain force onto the nonwoven webs, which typically enwrap and encompass the superabsorbent polymer particles. Consequently, the nonwoven webs will also elongate in order to accommodate for the additional space needed by the swelling superabsorbent polymer particles within the absorbent core.
It has been found that an elongated and somewhat strained absorbent core, when incorporated in a disposable diaper, which has been attached onto a wearer, may result in a strained appearance of the backsheet, leading e.g. to the formation of tension lines or wrinkles. Such tensed appearance may give raise to concerns by wearers or—if the wearers are babies or toddles—by the caretakers regarding the overall quality and especially the capacity of the disposable diaper. The tensed appearance may be perceived as an indication that the disposable diaper has reached its maximum load and needs to be replaced even if in fact a considerable amount of absorbent capacity is still available. The caretakers or wearers may thus attempt to change the diaper even if the absorbent core may still have the capacity to absorb further gushes of urine.
There is thus a need for disposable diapers with absorbent cores having high amounts of superabsorbent polymer particles and little to no airfelt, wherein, when only partly loaded with liquid, the backsheet may not have a strained appearance, especially when attached onto a wearer.